Soldering apparatus

ABSTRACT

Soldering apparatus comprising a sump for receiving molten solder covered with a layer of oil compound. A fountain is disposed centrally in the sump and forms a chamber having an inlet disposed in the molten solder and an upwardly opening outlet disposed centrally in the sump and elevated above the surface of the oil compound. A pump is provided for pulling molten solder in through the inlet and discharging it out the outlet to form a wave over which, for example, printed circuit boards may be passed to solder a plurality of components thereto and form electrical leads between the components. The pump circulates the molten solder through the fountain and out the outlet at a rate sufficient to cause it to spill downwardly around the fountain to pass through the layer of oil compound and carry a sufficient quantity of such oil compound therewith and into the inlet of the fountain to provide a desired ratio of oil compound to solder in the wave.

United States Patent {72] Inventor Robert D. Fitzsimmons North Reading, Mass. [2]] Appl. No. 782,824 [22] Filed Dec. 11, 1968 [45] Patented June 29, 19711 [73] Assignee State Street Bank and Trust Company Boston, Mass.

[54] SOLDERING APPARATUS 5 Claims, 7 Drawing Figs.

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[56] References Cited Primary Examiner-John F. Campbell Assistant Examiner-11. J. Craig A!t0rney- Fu1wider, Patton, Rieber, Lee & Utecht ABSTRACT: Soldering apparatus comprising a sump for receiving molten solder covered with a layer of oil compound. A fountain is disposed centrally in the sump and forms a chamber having an inlet disposed in the molten solder and an upwardly opening outlet disposed centrally in the sump and elevated above the surface of the oil compound. A pump is provided for pulling molten solder in through the inlet and discharging it out the outlet to form a wave over which, for example, printed circuit boards may be passed to solder a pluralit'y of components thereto and form electrical leads between the components. The pump circulates the molten solder through the fountain and out the outlet at a' rate sufi'lcient to cause it to spill downwardly around the fountain to pass through the layer of oil compound and carry a sufficient quantity of such oil compound therewith and into the inlet of the fountain to provide a desired ratio of oil compound to solder in the wave.

PATENTEUJUNZQIQYI 3 5 9 59 sum 1 or 2 INVENTOR. 20:52 7' D. firzs/uMo/vs Arra /V915 SOLDERING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to devices for sol dering components together.

2. Description of Prior Art Prior art soldering devices have been proposed for intermixing an oil compound and molten solder to reduce dripping from the soldered component during solidification and consequent icicling and bridging, and also reducing oxidization and consequent formation of a film, or dross, on the surface of the solder. These devices generally include a sump having molten solder therein and covered with a layer of oil compound. A fountain is provided which includes a first inlet disposed in the solder and a second inlet disposed in the oil compound and the ratio of the resultant solder-oil compound mix is controlled by valve means. A device of this type is shown in US. Pat. No. 3,058,441. Such devices suffer the shortcoming of including a pair of inlets for the fountain and valve means must be provided for controlling the ratio of oil compound to solder. Valves located in the oil compound conduits frequently have oil baked on the seats thereof during operation of the devices thereby changing the oil flow rate and altering the ratio ofoil to colder thus resulting in'improper soldering of components passed through the wave. Further, the depth and vertical location of the layer ,of oil compound floating on the solder must be maintained rather accurately to avoid introducing either air or solder into the oil compound inlet.

SUMMARY OF THE INVENTION The present invention is characterized by a sump containing molten solder covered by a layer of oil compound. A fountain is disposed in the sump and includes an inlet disposed in the solder, and an upwardly facing outlet disposed above the oil compound. A pump draws solder in said inlet and discharges it out said outlet at a rate which causes the expelled solder to flow downwardly through the oil compound in the sump at a rate sufficient to pull sufficient oil compound therewith, and into the inlet, to form the desired oil-compound-to-solder ratio in the resultant soldering wave formed above the outlet.

An object of the present invention is to provide soldering apparatus which will thoroughly intermix solder and oil to prevent icicling and provide for well-defined electrical leads on printed circuit boards.

A further object of the present invention is to provide a soldering apparatus of the type described which does not require a valve for controlling the oil-to-solder ratio.

Another object of the present invention is to provide soldering apparatus of the type described which includes a pump for circulating the solder through the oil compound at a rate which will create a mixture containing the desired ratio of oil compound to solder.

The objects and advantages of the present invention will become apparent from consideration of the following description when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a soldering apparatus embodying the present invention;

FIG. 2 is top view of the soldering apparatus shown in FIG.

FIG. 3 is a partial top view, in enlarged scale, of the soldering apparatus shown in FIG. I;

FIG. 4 is a broken vertical sectional view, in enlarged scale, taken along the line 4-4 of FIG. 3; FIG 5 is a vertical'sectional view in enlarged scale, take along the line 55 of FIG. 2;

FIG. 6 is a plan view taken along the line 6-6 of FIG. 5; and

FIG. 7 is a vertical sectional view taken along the line 7-7 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT The soldering apparatus of present invention includes a cabinet, generally designated Ill, which supports a sump I3 (FIG. 5) containing molten solder 15 covered by a layer of oil compound or wetting agent 17. Disposed centrally in the sump 13 is a fountain, generally designated 39, which receives solder l5 and oil compound 17 from a pump 21 having inlets 23 which are disposed within the solder 15. The fountain I9 is formed with an upwardly facing opening 25 over which is formed a molten solder wave 29. Thus, the pump 21 may be operated to pull solder 15 in through the inlets 23 to force such solder into the fountain l9 and upwardly out the opening 25 to form the wave 29. The solder 115 will be pumped at a sufficient rate to cause the solder spilling downwardly about the outer periphery of the fountain 119 to pull a selected amount of oil compound 17 therewith and into the inlets 23 to form a mixture having the desired ratio of oil compound 17 to solder R5 for forming the wave 25?.

Referring to FIG. 7, the sump I3 is supported from the cabinet III by means of mounting brackets 35 and 37. Referring to FIG. 5, the pump 21 is in communication with the right-hand end of the fountain 19 by means ofa pipe 29 which forms a discharge port 41 within a plenum chamber 38 formed by such fountain 19. The fountain 19 includes a pair of upright end walls 412 and 44, and a pair ofsidewalls 4 3 and 45 (FIG. 7) which slope upwardly and inwardly to form the outlet 25 between their upper edges.

A plurality of vertical and horizontal walls from vertical and horizontal baffles 47 and 49, respectively, for interrupting smooth laminar flow of the molten solder and oil compound 17 to form a wave of uniform height above the top baffle 49. As best seen in FIG. 7, electric heaters 50 are secured to the bottom wall and sidewalls of the sump 113 for maintaining the solder 15 heated to the desired temperature.

An inclined conveyor, generally designated 51, is supported across the top of the fountain l9 and includes a pair of opposed conveyor chains, generally designated 53, carried in respective longitudinal tracks 55. Referring to FIG. 4, the conveyor chains 53 include chain links 57 which mount opposed holding fingers 59 for receiving carrier trays, generally designated 61. The chains 53 thread over sprockets (not shown) disposed at opposite ends of the tracks 55 and the sprockets at the upper end of the conveyor 5i are driven by a motor housed within a housing 63.

The carrier 61 includes a rectangular frame 65 which has a longitudinal backing bar 67 mounted thereon. The backing bar 67 is formed on its opposite ends with outwardly facing notches which receive the frame 65 and have setscrews 71 for being tightened against the frame 65 to hold such backing bar 67 in position on the frame. A holding bar 77 is arranged coextensive with the backing bar 67 and is formed on its opposite extremities with outwardly facing notches which loosely fit the frame 65. Referring to FIG. 4, both the bar 67 and 77 )FIG. 4) are formed with confronting, longitudinal grooves 81 which receive the opposite edges of printed circuit boards 83.

Still referring to FIG. 3, a formed leaf springs, generally designated 82, is mounted on the frame 65 behind the holding bar 77 and includes a pair of arcuate portions 54 which press thereagainst.

The lower end of the conveyor 51 is supported on a pair of legs 85 and has a fluxer 37 disposed thereunder. The fluxer 87 is of conventional construction and may include brushes for applying flux to the circuit boards 83 as they are moved up the conveyor 5i. Disposed intermediate the fluxer 87 and the cabinet III is a preheater 91 which preheats the printed circuit boards 33 prior to application of the solder wave 29. The controls for the solder pump 21, conveyor speed and preheater 87 are all contained in a compact control console 90 which may be conveniently and rapidly replaced in case of failure.

In operation, the sump 13 is filled to the desired level with molten solder I5 and such solder is covered with a layer of oil compound 17. The fluxer 87, preheater 91 and pump 21 are started and the conveyor 51 actuated. The pump 21 pulls molten solder through the inlets 23 and passes it out the discharge port 41 into the fountain 19 where it is forced through the vertical baffles 47 and upwardly through the horizontal baffles 49. The upwardly expelled solder and oil compound mixture forms the wave 29 and then spills downwardly along the outer periphery of the sidewalls 43 and 45 to pass through the layer of oil compound 17 and back through the molten solder 15. The mixture passing down through the oil compound 17 pulls a portion thereof downwardly and introduces it into the pump inlet 23 for passage through the impeller of the pump 21 for thorough mixing and subsequent discharge back into the fountain 19. The pump 21 is operated at a speed which will circulate the solder at a rate which will effect the desired ratio of oil compound 17 to solder 15.

The components (not shown) have been previously mounted on the boards 83 and such boards etched to define the circuitry. The backing bar 67 on the carrier 61 has also been adjusted for the width of the circuit boards 83 to be printed and such boards are placed in the carrier by inserting one edge thereof in the groove 81 formed by the biased holding bar 77 and pressing that member against the bias of the spring 82 to enable the opposite edge thereof to be received within the groove 81 of the holding bar 67. The carrier 61 is then placed on the lower end of the conveyor 51 and will be passed over the fluxer 87 and preheater 91. The boards 83 are then passed over the wave 29 formed by the combination oil compound 17 and solder 15 to apply the desired solder.

From the foregoing description, it will be apparent that the soldering apparatus of present invention provides an economical and convenient means for soldering of electrical components. The ratio of solder to oil compound is controlled by pump rate and there is no requirement for maintaining the layer of soldering agent at any one particular level. Further, a carrier is provided for convenient receipt of a circuit board and rapid release thereof.

Various modifications and changes may be made with regard to the foregoing detailed description without departing from the spirit of the invention:

lclaim:

1. Soldering apparatus for producing a standing wave formed by a mixture of a selected ratio of oil compound and molten solder, said apparatus comprising:

a sump;

molten solder in said sump;

a layer of oil compound floating on said solder;

fountain means in said sump including a passage having an inlet disposed in said molten solder and an upwardly opening outlet disposed above the surface of said oil compound, said inlet being disposed a sufficient distance below the surface of said oil compound such that pumping ofsaid molten solder and oil compound out said outlet at a predetermined rate will cause the stream of molten solder pouring downwardly from said outlet to agitate said oil compound and intermix therewith sufficiently to produce a mixture of said selected ratio at said inlet; and

a pump for pumping said mixture through said passage at said predetermined rate.

2. Soldering apparatus as set forth in claim 1 that includes:

baffles arranged in said outlet to interrupt flow of said mixture and provide a uniform wave above said outlet.

3. Soldering apparatus as set forth in claim 1, that includes:

a heater disposed in heat exchange relationship with said sump for heating said molten solder.

4. Soldering apparatus as set forth in claim 1 that includes:

a plurality of vertically spaced horizontal walls, said walls including perforations for passage of said solder-and-oil compound to interrupt flow thereof and provide a uniform wave above said outlet.

5. Soldering apparatus as set forth in claim 1 wherein:

said pump includes a variable-speed drive means for varying the flow rate of said pump to adjust the ratio of solder to oil compound. 

1. Soldering apparatus for producing a standing wave formed by a mixture of a selected ratio of oil compound and molten solder, said apparatus comprising: a sump; molten solder in said sump; a layer of oil compound floating on said solder; fountain means in said sump including a passage having an inlet disposed in said molten solder and an upwardly opening outlet disposed above the surface of said oil compound, said inlet being disposed a sufficient distance below the surface of said oil compound such that pumping of said molten solder and oil compound out said outlet at a predetermined rate will cause the stream of molten solder pouring downwardly from said outlet to agitate said oil compound and intermix therewith sufficiently to produce a mixture of said selected ratio at said inlet; and a pump for pumping said mixture through said passage at said predetermined rate.
 2. Soldering apparatus as set forth in claim 1 that includes: baffles arranged in said outlet to interrupt flow of said mixture and provide a uniform wave above said outlet.
 3. Soldering apparatus as set forth in claim 1, that includes: a heater disposed in heat exchange relationship with said sump for heating said molten solder.
 4. Soldering apparatus as set forth in claim 1 that includes: a plurality of vertically spaced horizontal walls, said walls including perforations for passage of said solder-and-oil compound to interrupt flow thereof and provide a uniform wave above said outlet.
 5. Soldering apparatus as set forth in claim 1 wherein: said pump includes a variable-speed drive means for varying the flow rate of said pump to adjust the ratio of solder to oil compound. 